During refueling of a vehicle, fuel vapor is displaced from the fuel tank by the entering fuel. To prevent the displaced fuel vapors from entering the atmosphere, they are adsorbed in a canister containing a carbon charge. The canister is fluidly connected to the fuel tank and receives the fuel vapors as they are displaced. The carbon charge is an adsorbent material which adsorbs the fuel vapors.
After the fueling operation, the adsorbent loaded with fuel vapor can be desorbed as vapor in a purge cycle and is drawn by suction to the engine during an intake cycle where it is recovered for combustion. Motorists sometimes fill their tank to excess by “topping off” the fuel tank. This can cause liquid fuel to be sent to the canister where, if it enters the canister, it causes the carbon charge performance to be degraded so that vapors can no longer be adsorbed.